50ml (1¾fl oz) semillon verjus or other white verjus
50ml (1¾fl oz) Korean fermented plum extract
Soak the umeboshi in 1litre (35fl oz) of cold water overnight. Drain and rinse well. Place the umeboshi, verjus and fermented plum extract in a small saucepan and cook gently over low heat until almost all of the liquid has evaporated.
Put the remaining contents of the saucepan in a drum sieve and push the flesh and juices through, discarding the seeds.